The invention relates to methods for polymerizing a monomer enzymatically in the presence of a template to form a polymer-template complex.
Recently, there has been an increased interest in the tailored development of certain classes of polymers, such as electrically conductive and optically active polymers (e.g. polythiophene, polypyrrole, and polyaniline) for application to wider ranges of use. Examples of such uses include light-weight energy storage devices, electrolytic capacitors, anti-static and anti-corrosive coatings for smart windows, and biological sensors. However, the potential applications of these polymers have been limited by some fundamental properties of the monomers employed to form these polymers and by limitations of known polymerization techniques.
Electrically conductive and optically active polymers are relatively insoluble in water. Therefore, these polymers are typically formed in an organic solvent. Attempts to increase the water solubility of these polymers have included derivatization of the monomer before polymerization or the resulting polymer formed. However, derivatization of monomers typically slows polymerization, while derivatization of polymers generally causes some degradation.
Moreover, the physical properties of polymeric materials generally can be manipulated only by mechanical means such as extrusion, or by polarization of relatively short polymers or oligomers in an electric field. Further, the existing synthetic methods of forming polymers generally do not provide means for manipulating their shape during polymerization.
Therefore, a need exists to overcome or minimize the above-referenced problems associated with polymer synthesis.
The invention relates to novel methods for enzymatic polymerization which include (1) obtaining a reaction mixture including a monomer, a template, and an enzyme, and (2) polymerizing the monomer aligning along the template to form a polymer-template complex. Not only does such a complex possess high molecular weight, high water solubility, and exceptional electrical and optical properties, its preparation is also simple, environmentally friendly, and inexpensive. Its excellent properties enable the complex to be used in many applications. For example, polyaniline-lignin sulfonate complexes can be used as an emulsifier in asphalt, or a dispersant for cement mixes, fertilizers, linoleum paste, dust suppressants, dyes and pigments. As another example, new polyaniline-micelle complexes, which form a spherical polymer shell, can be used for paints, coatings, and also for entrapping and transporting materials, e.g., pharmaceuticals, that are generally insoluble in aqueous media.
One aspect of this invention relates to novel methods for enzymatic polymerization. The methods include obtaining a reaction mixture including a monomer (e.g., aniline or phenol), a micelle (e.g., a micelle template with positively charged or negatively charged groups on the surface), and an enzyme (e.g., a peroxidase such as horseradish peroxidase); and incubating the reaction mixture for a time and under conditions sufficient for the monomer to align around the micelle surface and polymerize to form a polymer-micelle complex. The method further includes combining an electron acceptor, such as hydrogen peroxide, with the reaction mixture to initiate the polymerization. The reaction mixture in the novel method has a pH of between about 4 and about 10 (e.g., between about 6 and about 8).
The micelles used in the novel methods include multiple units. Each unit has a hydrophobic part and a hydrophilic part. The hydrophilic part includes an aromatic ring (e.g., benzene) bonded to an acidic substituent (e.g., sulfonate) with a pKa of the acidic substituent ranging from 0.5 to 3.5 (e.g., 0.5 to 2.5). Some examples of such a micelle unit are dodecyl benzene sulfonic acid, octadecyl benzene sulfonic acid, and hexadecyl naphthyl sulfonic acid.
Another aspect of this invention relates to novel polymer-micelle complexes including a polymer bound to a micelle. The novel complexes have a molecular weight ranging from 70 kD to 10,000 kD (e.g., 100 kD to 7,000 kD) and can be electrically conducting and/or water soluble. The novel complexes can also be optically active. An example of the novel complex is polymer-dodecyl benzene sulfonic acid (e.g., polyaniline-dodecyl benzene sulfonic acid or polyphenol-dodecyl benzene sulfonic acid).
A further aspect of this invention relates to a novel method for enzymatic polymerization. The method includes obtaining a reaction mixture including a monomer (e.g., aniline or phenol), a template, and an enzyme (e.g., a peroxidase such as horseradish peroxidase); and incubating the reaction mixture for a time and under conditions sufficient for the monomer to align along the template and polymerize to form a polymer-template complex. The method further includes combining hydrogen peroxide with the reaction mixture to initiate the polymerization. The reaction mixture in the novel method has a pH that is greater than 4 (e.g., between about 4 and about 10 or between about 6 and about 8).
The template can be lignin sulfonate or a borate-containing polyelectrolyte; both of which contain charged groups (i.e., sulfonate or borate) that are responsible, at least in part, for aligning the charged monomers. Borate-containing polyelectrolytes can be a polymer (e.g., polyvinyl) containing positively or negatively charged groups. Examples of such charged groups include trifluoroborate [xe2x80x94BF3]xe2x88x92, trimethylborate [xe2x80x94B(CH3)3]xe2x88x92, and hydrobis(pyridine)boron [xe2x80x94BH(C5H5N)2]+.
A still further aspect of this invention relates to novel polymer-template complexes including a polymer bound to a template. The novel complexes have a molecular weight ranging from 70 kD to 10,000 kD (e.g., 100 kD to 7,000 kD). The complexes can be electrically conducting and/or water soluble and can act as a charge-transfer complex or an optically active complex. Examples of the novel complexes include polymer-lignin sulfonate (e.g., polyaniline-lignin sulfonate or polyphenol-lignin sulfonate) and polymer-borate-containing polyelec-trolyte (e.g., polyaniline-tetrafluoroborate-containing polyelectrolyte or polyphenol-tetramethylborate-containing polyelectrolyte).
A template binds to and aligns the monomers so as to maximize conjugation and minimize branching of the polymers formed according to the new methods. The template can be a polyelectrolyte. The template can also be a micelle, an oligomer, or a polymer. Examples of suitable templates include an azo polymer, a substituted polystyrene, a substituted vinyl polymer (e.g., polyvinyl phosphonate, polyvinyl phosphate, or polyvinyl benzoic acid), a sulfonated polymer (e.g., lignin sulfonate, sulfonated polystyrene, or polystyrene sulfonic acid), a polynucleotide (e.g., deoxyribonucleotide or ribonucleotide), a polypeptide, a protein, a biological receptor, a zeolite, a caged compound, an azopolymer, an vinyl polymers (e.g., polyvinyl benzoic acid, polyvinyl phosphate, or polyvinyl borate), polyphenol red, azo compounds, a dendrimer, a protein, or sulfonated micelles (e.g., micelle containing dodecyl benzene sulfonic acid ). The template can be positively charged, such as a polycation (e.g., poly(diallyl dimethyl ammonium chloride)) or negatively charged, such as a polyanion (e.g., sulfonated polystyrene). It is important that the charged groups of a template are indeed in their charged form under the required reaction conditions. For example, in the case of a polyanionic template (e.g., lignin sulfonate), the pKa value of the anionic functionalities (e.g., sulfonate) should be sufficiently low (e.g., from about 0.5 to about 3.5) to ensure that they are negatively charged under the reaction conditions (e.g., pH 4.0 to 10.0) so as to bind to and align the positively charged aniline monomers.
A conducting polymer refers to a polymer which exhibits conductivity ranging from about 10xe2x88x9210 to 106 S/cm.
The new template-assisted enzymatic polymerization reactions address problems associated with existing methods of preparing electrically conductive polymers such as the need for harsh chemicals, high costs, difficulty in producing polymeric products with high water solubility and electrical conductivity, and the inability to control shapes and sizes of such products. The polymer-template complexes prepared by this novel polymerization, in addition to being electrically conductive and completely soluble in aqueous media, are also of high molecular weights (e.g.,  greater than 70 kD).
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict in terminology, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.
Other features and advantages of the invention will be apparent from the following detailed description, and from the claims.